Transient protection and current control of devices

ABSTRACT

An apparatus including an electrical device electrically coupled to a power source and transient suppression and current control circuitry electrically coupled to the electrical device. The circuitry includes a negative temperature coefficient thermistor electrically coupled between the power source and the electrical device and being responsive to an electrical power surge condition to dissipate at least a portion of the power associated with the surge. The circuitry also includes a positive temperature coefficient thermistor electrically coupled between the power source and the electrical device and being responsive to a change in electrical current to maintain the electrical current below an acceptable threshold level.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of pending U.S. patentapplication Ser. No. 10/617,641 filed on Jul. 11, 2003, the contents ofwhich are incorporated herein by reference.

BACKGROUND

The present invention relates to transient protection and currentcontrol of various devices, and more particularly but not exclusivelyrelates to the utilization of temperature sensitive devices to eliminateor at least reduce any adverse consequences caused by power surges andincreased current levels on various devices.

It is frequently desirable to interface various devices, such as sensorassemblies, to controllers. In many instances, the controller interfaceprovides electrical power to operate such devices. Unfortunately, thisarrangement sometimes generates transients that can damage the device orother circuit components connected to the controller. A similar problemcan result when powering the device with a dedicated power supply orother source. Typically, general-purpose surge protectors are notadequate to provide the desired level of circuit protection. Moreover,increased current levels that are sometimes caused by an internal dropin circuit resistance may lead to excessive current levels that candamage the device, the controller, or other circuit components connectedto the controller. Accordingly, there is a need for furthercontributions in this area of technology.

SUMMARY

One embodiment of the present invention is a unique technique fortransient protection and current control of various devices including,for example, sensor assemblies. Other embodiments include uniquesystems, devices, apparatus, and methods for protecting such devicesfrom transients and excess current levels.

One embodiment of the invention includes a sensor operable to detect oneor more physical characteristics and a transient suppression and currentcontrol circuit electrically coupled between a power source and thesensor. This circuit includes at least one thermistor that is responsiveto an electrical power surge condition to dissipate at least a portionof the power associated with the surge, and at least one thermistor thatis responsive to a change in electrical current to maintain theelectrical current below a threshold level.

In another embodiment of the invention, an apparatus includes anelectrical device electrically coupled to a power source and transientsuppression and current control circuitry electrically coupled to theelectrical device. The circuitry includes a first negative temperaturecoefficient thermistor electrically coupled between the power source andthe electrical device and being responsive to an electrical power surgecondition to dissipate at least a portion of the power associated withthe surge, and a first positive temperature coefficient thermistorelectrically coupled between the power source and the electrical deviceand being responsive to a change in electrical current to maintain theelectrical current below a threshold level.

In another embodiment of the invention, a method is directed toproviding transient suppression and current control which includesproviding electrical power to an electrical device, suppressing atransient power surge by dissipating at least a portion of the surgeusing a negative temperature coefficient thermistor, and maintainingelectrical current below a threshold level using a positive temperaturecoefficient thermistor.

In another embodiment of the invention, an apparatus includes anelectrical device, a connector configured to electrically couple theelectrical device to a power source, and first and second thermistorselectrically coupled between the connector and the electrical device,with one of the first and second thermistors being responsive to anelectrical power surge condition to dissipate at least a portion of thepower associated with the surge, and with another of the first andsecond thermistors being responsive to a change in electrical current tomaintain the electrical current below a threshold level.

In another embodiment of the invention, a system includes a sensoroperable to detect a change in one or more physical characteristics andto provide a corresponding sensor signal, a controller including a powersource electrically coupled to the sensor, and transient suppression andcurrent control circuitry electrically coupled between the sensor andthe power source of the controller. The circuitry includes a firstnegative temperature coefficient thermistor responsive to an electricalpower surge condition to dissipate at least a portion of the electricalpower associated with the surge, and a first positive temperaturecoefficient thermistor responsive to a change in electrical current tomaintain the electrical current below a threshold level.

It is one object of the present invention is to provide a uniquetechnique for transient protection and current control associated withvarious devices including, for example, sensor assemblies.

Another object is to provide a unique system, method, device, orapparatus for protecting various devices from transients and increasedcurrent levels.

Other objects, embodiments, forms, features, advantages, aspects andbenefits of the present invention shall become apparent from thedetailed description and drawings included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a system according to one embodiment ofthe present invention which includes a device having transientsuppression circuitry.

FIG. 2 is a schematic view of the device of FIG. 1 shown in greaterdetail.

FIG. 3 is a schematic view of a system according to another embodimentof the present invention which includes a device having transientsuppression and current control circuitry.

FIG. 4 is a schematic view of the device of FIG. 3 shown in greaterdetail.

DETAILED DESCRIPTION

While the present invention may be embodied in many different forms, forthe purpose of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is hereby intended. Any alterations and further modificationsin the described embodiments, and any further applications of theprinciples of the invention as described herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

In one embodiment of the present invention, a sensing device is used todetect one or more physical characteristics. The sensing device iselectrically coupled to a controller and a power source. The powersource can be included in the controller. The connection of the sensingdevice to the controller is made through a corresponding interface. Thecontroller is further connected electrically to an output device. Thecontroller receives input from the sensing device and generates anoutput, which is sent to the output device. Transient suppression and/orcurrent control circuitry is utilized in the connection between thesensing device and the controller. The circuitry utilizes thermistors tosuppress power surges and/or to maintain current levels below certainthreshold levels.

Referring to FIG. 1, shown therein is one embodiment of the presentinvention that is directed to a system 20 including controller 30,output device 40, and sensing device 50. Sensing device 50 iselectrically coupled to sensing interface 32 of controller 30.Controller 30 is electrically coupled to output device 40.

FIG. 2 depicts controller 30 and sensing device 50 of FIG. 1 in moredetail. Sensing device 50 includes sensor assembly 52 coupled toconnector 54. Sensing interface 32 includes electrical power source 34,which is operable to supply electrical power to sensing device 50.Interface 32 electrically couples to connector 54 of sensing device 50.Assembly 52 and connector 54 are provided as an integral sensing deviceunit 56. Sensor assembly 52 includes transient suppression circuitry 60,sensing circuitry 74, and indicators 72. Transient suppression circuitry60 includes two negative temperature coefficient thermistors 62, thatare more specifically designated thermistors T1 and T2. Indicators 72 ofassembly 52 are more specifically designated indicators I1 and I2.Sensing circuitry 74 includes sensor 70. Sensor 70 is operable to detectone or more physical characteristics relative to its environment in astandard manner.

Sensor 70 is connected in series with thermistor T2 of transientsuppression circuitry 60. Indicators 72 are electrically connected inparallel between sensor 70 and thermistor T1. Each individual thermistor62 is connected to a different contact, and correspondingly a differentelectrical node, of connector 54. This connection topology results intwo distinct electrical branches of circuitry 60, each having adifferent one of thermistors 62.

Referring generally to FIGS. 1 and 2, sensor 70 of circuitry 74 isoperable to detect one or more physical characteristics when poweredthrough connector 54 with power source 34. One example of a physicalcharacteristic that can be detected with sensor 70 is the occurrence ofa change in a magnetic field. Alternatively or additionally, sensor 70can be operable to detect temperature, electrical conductivity,pressure, velocity, acceleration, pH, intensity of one or morewavelengths of electromagnetic radiation, acoustic vibration, and/ormass fluid flow, to name just a few nonlimiting examples. Signalsrepresentative of detected physical characteristics are output fromsensor 70 to indicators 72, and through transient suppression circuitry60 and connector 54 to controller 30. Indicators 72 respond to a desiredchange in the sensor signal to display appropriate data to a user ofsystem 20. In one arrangement, one of indicators 72 is arranged toindicate that device 50 is properly connected to and powered bycontroller 30 via interface 32 and the other of indicators 72 indicateswhen sensor 70 detects a characteristic level that exceeds a desiredthreshold. In a further embodiment, one or more of indicators 72 isactivated to indicate a failure condition. In other embodiments,indicators 72 can be differently arranged, including more or fewerindicators. In one alternative, indicators 72 are absent with sensor 70being electrically coupled in series between thermistors T1 and T2.

Controller 30 receives signals from sensor 70, and selectively transmitsan output signal to output device 40 in response thereto. In onenonlimiting example, controller 30 is a programmable logic controllerand output device 40 is a power relay that is activated when acharacteristic detected with sensor 70 exceeds a desired level. For thisembodiment, device 50 operates as a discrete, two-state device. In otherembodiments, device 50 can be configured to operate in more than twodiscrete states and/or in a continuous manner over one or morecontinuous ranges of values.

Source 34 (included in controller 30) supplies electrical power tosensing circuitry 74 via transient suppression circuitry 60. Both thedetection signals from sensor 70 and electrical power are transferredalong the same electrical pathways through transient suppressioncircuitry 60. Fluctuation in the power supplied to controller 30, achange in operating state of controller 30, connection or disconnectionof unit 56 from interface 32, shifts in one or more environmentalcharacteristics (such as temperature), device failures, and the like cancause transient increases in power output from source 34 to device 50via interface 32 and connector 54. In one particular example, atransient results from initially powering device 50 through interface32, which abruptly provides an electric potential to assembly 52.Sensing circuitry 74 and sensor 70 may be susceptible to damage by suchtransient power surges. Transient suppression circuitry 60 is utilizedto protect sensing circuitry 74 from power surges, including but notlimited to, power surges that can result when cycling electrical powerto system 20, including device 50 or some part thereof.

Transient suppression circuitry 60 utilizes thermistors 62 of a negativetemperature coefficient type to suppress power surges. Prior to applyingpower to sensing device 50 from electrical power source 34, sensingdevice 50 and thermistors 62 are typically at or near ambient roomtemperature. When at or near room temperature, thermistors 62 arecharacterized by high electrical resistance. Thus, when power is appliedto sensing device 50, the high electrical resistance of thermistors 62dissipates power surges encountered by thermistors 62, thus protectingsensor 70. As energy flows through thermistors 62, the temperature ofthermistors 62 increases. The increase in temperature of the thermistors62 results in decreased electrical resistance. Thus, after sensingdevice 50 reaches a desired operating temperature, the electricalresistance in thermistors 62 decreases allowing signals from sensor 70to be provided to controller 30 without undesired interference fromtransient suppression circuitry 60.

Although the operation of system 20 has been described utilizingnegative coefficient thermistors, other thermistor types may be utilizedin which electrical resistance is initially low at room/startingtemperature to shunt power around the sensor device or devices to beprotected from transients, and then electrical resistance is increasedto allow sufficient current for operation of sensor 70 at a desiredtemperature. In still other embodiments, a combination of differentthermistor types can be utilized. In one preferred embodiment, transientsuppression circuitry 60 is capable of suppressing power surges having aduration of at least 250 microseconds and a peak current of at least 500milliamperes. In a more preferred embodiment, transient suppressioncircuitry 60 is capable of suppressing a power surge of up to 500microseconds and a peak current of up to 1 ampere. Nonetheless, in otherembodiments, a different power surge suppression capability is provided.

Transient suppression circuitry 60 can be utilized with different typesof electrical power sources. For example, transient suppressioncircuitry 60 can be utilized with alternating current or direct currentpower sources. The utilization of two thermistors 62 in the mannerillustrated provides for the suppression of power spikes originatingfrom either electrical node of connector 54 before reaching sensor 70.In embodiments where it is desired to suppress spikes through only oneof these nodes, only a respective one of thermistors 62 may be utilized.In other embodiments of the invention, one or more of connector 54,circuitry 74, and/or indicators 72 is separate from one or more otherportions of device 50 such that they are not collectively provided as anintegral operating unit 56. Alternatively or additionally, power source34 and/or interface 32 can be separate from controller 30 in furtherembodiments.

Referring to FIG. 3, shown therein is another embodiment of the presentinvention which is directed to a system 120 including a controller 130,an output device 140, and an electrical device 150. Electrical device150 is electrically coupled to interface 132 of controller 130.Controller 130 is electrically coupled to output device 140.

FIG. 4 depicts controller 130 and electrical device 150 of FIG. 3 inmore detail. In one embodiment, electrical device 150 comprises an inputdevice configured to provide an input signal to the controller 130. In aspecific embodiment, the controller 130 comprises a programmable logiccontroller including a number of I/O cards. However, other types ofcontrollers and interfaces are also contemplated as would occur to oneof skill in the art, such as, for example, a computer or other types ofcomputing devices. In another specific embodiment, the input device 150comprises a sensing device configured to detect one or more physicalcharacteristics relative to its environment in a standard manner.However, it should be understood that other types of electrical devicesare also contemplated as falling within the scope of the presentinvention including, for example, various types of actuators,transducers, or other electrically driven devices. Interface 132includes electrical power source 134 which is operable to supplyelectrical power to input device 150. The power source 134 can be of thealternating type (AC) or the direct type (DC). The interface 132electrically couples to connector 154 of input device 150 in a standardmanner.

The sensor device 150 includes a sensor assembly 152 coupled toconnector 154. In one embodiment, sensor assembly 152 and possibly theconnector 154 are provided as an integral unit packaged within an outerbody or housing 156. Sensor assembly 152 includes transient suppressionand current control circuitry 160, sensing circuitry 174, and indicators172. Indicators 172 are also designated as I1 and I2. In one embodimentof the invention, transient suppression and current control circuitry160 includes two negative temperature coefficient thermistors 162 thatare also designated as NTC₁ and NTC₂, and two positive temperaturecoefficient thermistors 164 that are also designated as PTC₁ and PTC₂.In a specific embodiment, the thermistors 162, 164 are unipolar so as tosuppress both positive and negative incoming pulses. However, it shouldbe understood that other types, configurations and arrangements ofthermistors are also contemplated as would occur to one of skill in theart.

As will be discussed more fully below, the negative temperaturecoefficient thermistors NTC₁ and NTC₂ are electrically coupled betweenthe power source 134 of controller 130 and the sensing circuitry 174 ofinput device 150, and are responsive to an electrical power surgecondition to dissipate at least a portion of the power associated withthe surge. Additionally, the positive temperature coefficientthermistors PTC₁ and PTC₂ are also electrically coupled between thepower source 134 of controller 130 and the sensing circuitry 174 ofinput device 150, and are responsive to a change in electrical currentto maintain the electrical current below a threshold level.

In the illustrated embodiment, the first negative temperaturecoefficient thermistor NTC₁ and the first positive temperaturecoefficient thermistor PTC₁ are electrically connected in series betweenthe power source 134 and the sensing circuitry 174. Specifically, thefirst negative temperature coefficient thermistor NTC₁ is electricallyconnected to a first node of the power source 134, and the firstpositive temperature coefficient thermistor PTC₁ is electricallyconnected between the first negative temperature coefficient thermistorNTC₁ and the sensing circuitry 174. Additionally, the second negativetemperature coefficient thermistor NTC₂ and the second positivetemperature coefficient thermistor PTC₂ are electrically connected inseries between the power source 134 and the sensing circuitry 174.Specifically, the second negative temperature coefficient thermistorNTC₂ is electrically connected to a second node of the power source 134,and the second positive temperature coefficient thermistor PTC₂ iselectrically connected between the second negative temperaturecoefficient thermistor NTC₂ and the sensing circuitry 174. However, itshould be understood that other arrangements and positioning of thethermistors 162 and 164 are also contemplated as falling within thescope of the present invention.

In one embodiment of the invention, the negative temperature coefficientthermistors NTC₁ and NTC₂ are connected to a different contact, andcorrespondingly to a different electrical node, of connector 154. Thisconnection topology thereby results in two distinct electrical branchesof the transient suppression and current control circuitry 160, eachincluding a corresponding pair of negative and positive temperaturecoefficient thermistors. In a further embodiment of the invention, atleast one of the indicators 172 is electrically coupled in series withthe sensor 170 and the thermistors 162 and 164. In a specificembodiment, indicators 172 are electrically connected in parallelbetween sensor 170 and the first positive temperature coefficientthermistor PTC₁. However, it should be understood that otherarrangements and positioning of the thermistors 162 and 164, the sensor170 and/or the indicators 172 are also contemplated as falling withinthe scope of the present invention.

Referring generally to FIGS. 3 and 4, sensor 170 of circuitry 174 isoperable to detect one or more physical characteristics when poweredthrough connector 154 via power source 134. One example of a physicalcharacteristic that can be detected with sensor 170 is the occurrence ofa change in a magnetic field. Alternatively or additionally, sensor 170can be operable to detect temperature, electrical conductivity,pressure, velocity, acceleration, pH, intensity of one or morewavelengths of electromagnetic radiation, acoustic vibration, and/ormass fluid flow, to name just a few nonlimiting examples. Signalsrepresentative of detected physical characteristics are output fromsensor 170 to indicators 172, and through transient suppression andcurrent control circuitry 160 and connector 154 to controller 130.Indicators 172 respond to a desired change in the sensor signal todisplay appropriate data to a user of system 120. In one arrangement,one of indicators 172 is arranged to indicate that input device 150 isproperly connected to and powered by controller 130 via interface 132,and the other of indicators 172 indicates when sensor 170 detects acharacteristic level that exceeds a desired threshold. In a furtherembodiment, one or more of indicators 172 may be activated to indicate afailure condition. In other embodiments, indicators 172 can bedifferently arranged, including a single indicator or three or moreindicators. Additionally, in a further embodiment, indicators 172 areabsent and sensor 170 is directly coupled in series between positivetemperature coefficient thermistors PTC₁ and PTC₂.

Controller 130 receives signals from sensor 170 and selectivelytransmits an output signal to output device 140 in response thereto. Inone non-limiting example, controller 130 is a programmable logiccontroller and output device 140 is a power relay that is activated whena characteristic detected with sensor 170 exceeds a desired level. Forthis embodiment, device 150 operates as a discrete, two-state device. Inother embodiments, device 150 can be configured to operate in more thantwo discrete states and/or in a continuous manner over one or morecontinuous ranges of values. In still other embodiments, the outputdevice 140 may comprise a switch or an electrical component associatedwith a machine that is configured to perform some type of work.

The power source 134 (included in controller 130) supplies electricalpower to the sensing circuitry 174 via the transient suppression andcurrent control circuitry 160. The detection signals from the sensor 170and the electrical power from the source 134 are each transferred alongthe same electrical pathways, and more specifically through thetransient suppression and current control circuitry 160. Fluctuation inthe power supplied to controller 130, a change in operating state ofcontroller 130, connection or disconnection of unit 156 from interface132, shifts in one or more environmental characteristics (such astemperature), device failures, and the like can cause transientincreases in power output from source 134 to device 150 via interface132 and connector 154. In one particular example, a transient resultsfrom initially powering device 150 through interface 132, which abruptlyprovides an electric potential to the assembly 152. Sensing circuitry174, sensor 170 and/or other components or devices electrically coupledto the power source 134 may be susceptible to damage by such transientpower surges. The transient suppression and current control circuitry160 is utilized to protect sensing circuitry 174 from power surges,including but not limited to, power surges that can result when cyclingelectrical power to system 120, including input device 150 or some partthereof. As a result, the likelihood of damage and/or destruction of oneor more components associated with the input device 150 as a result ofoverheating is significantly reduced. Additionally, the circuitry 160 isconfigured and arranged to minimize current or voltage drop across theinput device 150.

Transient suppression and current control circuitry 160 utilizesthermistors 162 of a negative temperature coefficient type to suppresspower surges. Prior to applying power to input device 150 fromelectrical power source 134, input device 150 and the negativetemperature coefficient thermistors NTC₁ and NTC₂ are typically at ornear ambient room temperature. When at or near room temperature,thermistors NTC₁ and NTC₂ are characterized by a relatively highelectrical resistance. Thus, when power is applied to input device 150,the high electrical resistance associated with the thermistors NTC₁ andNTC₂ dissipates power surges encountered by thermistors 162, thusprotecting sensor 170 and indicators 172 from overheating and possibledamage or destruction. As energy flows through thermistors NTC₁ andNTC₂, the temperature of the thermistors increases. This increase in thetemperature of the thermistors 162 correspondingly results in decreasedelectrical resistance. Thus, after input device 150 reaches a thresholdoperating temperature, the electrical resistance in thermistors NTC₁ andNTC₂ decreases, thereby allowing signals from sensor 170 to be providedto controller 130 without undesired interference from transientsuppression and current control circuitry 160.

Although the operation of system 120 has been described utilizingthermistors of a negative coefficient type, other thermistor types maybe utilized in which electrical resistance is initially low atroom/starting temperature to shunt power around the sensor device ordevices to be protected from transients, and then electrical resistanceis increased to allow sufficient current for operation of sensor 170 ata desired temperature. In still other embodiments, a combination ofdifferent thermistor types and configurations can be utilized. In oneembodiment of the invention, transient suppression and current controlcircuitry 160 is capable of suppressing power surges having a durationof at least 250 microseconds and a peak current of at least 500milliamperes. In a further embodiment, transient suppression circuitry160 is capable of suppressing a power surge of up to 500 microsecondsand a peak current of up to 1 ampere. Nonetheless, in other embodiments,a different power surge suppression capability is provided.

As should now be appreciated, utilization of one or both of the negativetemperature coefficient thermistors NTC₁ and NTC₂ in the mannerillustrated and described above dissipates at least a portion of thepower associated with a power surge, thereby providing for thesuppression of power spikes or surges originating from the power source130 or other powered components before reaching sensor 170. Inembodiments where it is desired to suppress spikes through only one ofthe nodes of the power source 130 or the connector 154, only one of thenegative temperature coefficient thermistors NTC₁ and NTC₂ need beutilized.

As discussed above, the power source 134 supplies electrical power tothe sensing circuitry 174 via the transient suppression and currentcontrol circuitry 160. The detection signals from the sensor 170 and theelectrical power from the source 134 are each transferred along the sameelectrical pathways, and more specifically through the transientsuppression and current control circuitry 160. Under certaincircumstances, the current passing through the circuitry 160 to and/orfrom the sensing circuitry 174 may increase to a level that may causedamage or destruction to the sensing circuitry 174, the controller 130and/or any other electrical component in electrical communication withthe circuitry 160. For example, a drop in internal circuit resistancemay lead to an increase in the current levels passing through thesensing circuitry 170 and/or the controller 130. Additionally, increasedcurrent levels may be associated with the abnormal operation of thepower source 134, a change in the operating state of controller 130,shifts in one or more environmental characteristics (such astemperature) and/or device failures. The transient suppression andcurrent control circuitry 160 is thereby utilized to protect the sensingcircuitry 174, the controller 130 and/or any other electrical componentin electrical communication with the circuitry 160 from current levelsthat exceed an unacceptable threshold level.

Transient suppression and current control circuitry 160 utilizesthermistors 164 of a positive temperature coefficient type to controlcurrent flow and to maintain current levels below a threshold level thatmight otherwise lead to the damage and/or destruction of one or moreelectrical components that are in electrical communication with thecircuitry 160. Prior to applying power to input device 150 fromelectrical power source 134, input device 150 and the positivetemperature coefficient thermistors PTC₁ and PTC₂ are typically at ornear ambient room temperature. When at or near room temperature,thermistors PTC₁ and PTC₂ are characterized by relatively low electricalresistance. Thus, when power is applied to the input device 150, the lowelectrical resistance of the positive temperature coefficientthermistors PTC₁ and PTC₂ will not appreciably effect current flowto/from the sensing circuitry 174 and the controller 130. However, ifcurrent levels exceed a threshold level upon the initial application ofpower to the device 150, the resistance of the positive temperaturecoefficient thermistors PTC₁ and PTC₂ will increase to control thecurrent level passing therethrough. As a result, the circuitryassociated with the sensing circuitry 174 and/or the controller 130 isprotected from overheating and possible damage or destruction.

As current flows through the positive temperature coefficientthermistors PTC₁ and PTC₂, the temperature of the thermistors willincrease. This increase in the temperature will correspondingly resultin increased electrical resistance, thereby reducing the level ofcurrent passing through the positive temperature coefficient thermistorsPTC₁ and PTC₂. Thus, the thermistors PTC₁ and PTC₂ are responsive tochanges in electrical current to maintain the current level within anormal and acceptable range of current and below a select thresholdlevel to protect the components in electrical communication with thecircuitry 160 from damage or destruction (e.g., sensing circuitry 174and controller 130). The thermistors PTC₁ and PTC₂ thereby operate toprovide a relatively stable current level that does not exceed athreshold level over a large temperature range and without undesiredinterference from transient suppression and current control circuitry160.

As should now be appreciated, utilization of one or both of the positivetemperature coefficient thermistors PTC₁ and PTC₂ in the mannerillustrated and described above controls the amount of current passingtherethrough to maintain current below a threshold level, therebyprotecting the components electrically connected to the circuitry 160from unacceptably high current levels. In embodiments where it isdesired to control/maintain current levels through only one of the nodesof the power source 130 or the connector 154, only one of the positivetemperature coefficient thermistors PTC₁ and PTC₂ need be utilized.Although the operation of system 120 has been described utilizingthermistors of a positive coefficient type, other thermistor types maybe utilized in which electrical resistance is initially low atroom/starting temperature and which increases to control the level ofcurrent passing therethrough.

In one embodiment of the invention, the transient suppression andcurrent control circuitry 160 and the sensing circuitry 174, includingsensor 170 and indicators 172, are incorporated into an integral sensingpackage or operating unit. In a further embodiment, the connector 154may also be incorporated into the integral sensing package. However, itshould be understood that in other embodiments of the invention, one ormore of the transient suppression and current control circuitry 160, thesensing circuitry 174, and the connector 154 may be separate from oneanother such that they are not collectively provided as an integraloperating unit. Additionally, in one embodiment, the transientsuppression and current control circuitry 160 is located at a remotelocation relative to the controller 130. However, other embodiments arealso contemplated wherein the circuitry 160 is directly connected orpositioned in close proximity to the controller 130.

Any theory, mechanism of operation, proof, or finding stated herein ismeant to further enhance understanding of the present invention, and isnot intended to limit the present invention in any way to such theory,mechanism of operation, proof, or finding. While the invention has beenillustrated and described in detail in the drawings and foregoingdescription, the same is to be considered as illustrative and notrestrictive in character, it being understood that only selectedembodiments have been shown and described and that all equivalents,changes, and modifications that come within the spirit of the inventionsas defined herein or by the following claims are desired to beprotected.

1. An apparatus, comprising: an electrical device electrically coupledto a power source; and transient suppression and current controlcircuitry electrically coupled to the electrical device, including: afirst negative temperature coefficient thermistor electrically coupledbetween the power source and the electrical device and being responsiveto an electrical power surge condition to dissipate at least a portionof the power associated with the surge; and a first positive temperaturecoefficient thermistor electrically coupled between the power source andthe electrical device and being responsive to a change in electricalcurrent to maintain the electrical current below a threshold level. 2.The apparatus of claim 1, wherein the first negative temperaturecoefficient thermistor and the first positive temperature coefficientthermistor are electrically connected in series between a first node ofthe power source and the electrical device.
 3. The apparatus of claim 2,wherein the first negative temperature coefficient thermistor iselectrically connected to the first node of the power source and whereinthe first positive temperature coefficient thermistor is electricallyconnected between the first negative temperature coefficient thermistorand the electrical device.
 4. The apparatus of claim 1, wherein thetransient suppression and current control circuitry further includes asecond negative temperature coefficient thermistor electrically coupledbetween the power source and the electrical device and a second positivetemperature coefficient thermistor electrically coupled between thepower source and the electrical device.
 5. The apparatus of claim 4,wherein the second negative temperature coefficient thermistor and thesecond positive temperature coefficient thermistor are electricallyconnected in series between a second node of the power source and theelectrical device.
 6. The apparatus of claim 5, wherein the secondnegative temperature coefficient thermistor is electrically connected tothe second node of the power source and wherein the second positivetemperature coefficient thermistor is electrically connected between thesecond negative temperature coefficient thermistor and the electricaldevice.
 7. The apparatus of claim 1, wherein the electrical devicecomprises a sensor operable to detect one or more physicalcharacteristics and to provide a corresponding electrical sensor signal.8. The apparatus of claim 7, wherein the one or more physicalcharacteristics include a change in a magnetic field detectable with thesensor.
 9. The apparatus of claim 7, further comprising a controllerincluding the power source, the controller being responsive to thesensor signal.
 10. The apparatus of claim 9, further comprising anoutput device coupled to the controller, the controller being operableto provide an output signal to the output device in response to a changein the sensor signal.
 11. The apparatus of claim 7, wherein the sensorand the transient suppression and current control circuitry areincorporated into an integral sensing device unit.
 12. The apparatus ofclaim 7, further comprising at least one indicator electrically coupledto the sensor; and wherein the sensor and the at least one indicator areelectrically coupled in series with the first negative temperaturecoefficient thermistor and the first positive temperature coefficientthermistor.
 13. The apparatus of claim 1, further comprising acontroller including the power source; an output device coupled to thecontroller; and wherein the controller is responsive to a change in anelectrical output signal provided by the electrical device; and whereinthe controller provides a corresponding control signal to the outputdevice.
 14. The apparatus of claim 1, wherein the electrical device andthe transient suppression and current control circuitry are incorporatedinto an integral package assembly.
 15. A method of providing transientsuppression and current control, comprising: providing electrical powerto an electrical device; suppressing a transient power surge bydissipating at least a portion of the surge using a negative temperaturecoefficient thermistor; and maintaining electrical current below athreshold level using a positive temperature coefficient thermistor. 16.The method of claim 15, wherein the electrical device comprises asensing device; and wherein the method further comprises detecting achange in one or more physical characteristics with the sensing device.17. The method of claim 15, further comprising: coupling the electricaldevice and an output device to a controller; providing an input signalfrom the electrical device to the controller; and providing an outputsignal to the output device from the controller in response to an inputsignal from the electrical device.
 18. The method of claim 15, whereinthe suppressing is provided by a negative temperature coefficientthermistor; and wherein the maintaining is provided by a positivetemperature coefficient thermistor; and wherein the negative temperaturecoefficient thermistor and the positive temperature coefficient areconnected in series between the power source and the electrical device.19. The method of claim 18, further comprising packaging the electricaldevice and the thermistors within an integral package body.
 20. Anapparatus, comprising: an electrical device; a connector configured toelectrically couple the electrical device to a power source; and firstand second thermistors electrically coupled between the connector andthe electrical device, one of the first and second thermistors beingresponsive to an electrical power surge condition to dissipate at leasta portion of the power associated with the surge, another of the firstand second thermistors being responsive to a change in electricalcurrent to maintain the electrical current below a threshold level. 21.The apparatus of claim 20, wherein the first thermistor comprises afirst negative temperature coefficient thermistor and wherein the secondthermistor comprises a first positive temperature coefficientthermistor.
 22. The apparatus of claim 21, wherein the first negativetemperature coefficient thermistor and the first positive temperaturecoefficient thermistor are electrically connected in series between afirst node of the connector and the electrical device.
 23. The apparatusof claim 22, wherein the first negative temperature coefficientthermistor is electrically connected to the first node of the connectorand wherein the first positive temperature coefficient thermistor iselectrically connected between the first negative temperaturecoefficient thermistor and the electrical device.
 24. The apparatus ofclaim 22, further comprising a second negative temperature coefficientthermistor and a second positive temperature coefficient thermistor; andwherein the second negative temperature coefficient thermistor and thesecond positive temperature coefficient thermistor are electricallyconnected in series between a second node of the connector and theelectrical device.
 25. The apparatus of claim 24, wherein the secondnegative temperature coefficient thermistor is electrically connected tothe second node of the connector and wherein the second positivetemperature coefficient thermistor is electrically connected between thesecond negative temperature coefficient thermistor and the electricaldevice.
 26. The apparatus of claim 20, wherein the electrical devicecomprises a sensor operable to detect one or more physicalcharacteristics and to provide a corresponding electrical sensor signal.27. The apparatus of claim 26, further comprising: a controller operableto provide the power source and being responsive to the sensor signal;and an output device coupled to the controller; and wherein thecontroller is operable to provide an output signal to the output devicein response to a change in the sensor signal.
 28. The apparatus of claim20, wherein the electrical device and the first and second thermistorsare incorporated into an integral package body.
 29. The apparatus ofclaim 28, wherein the connector is incorporated into the integralpackage body.
 30. A system, comprising: a sensor operable to detect achange in one or more physical characteristics and to provide acorresponding sensor signal; a controller including a power sourceelectrically coupled to the sensor; and transient suppression andcurrent control circuitry electrically coupled between the sensor andthe power source of the controller, the circuitry including: a firstnegative temperature coefficient thermistor responsive to an electricalpower surge condition to dissipate at least a portion of the electricalpower associated with the surge; and a first positive temperaturecoefficient thermistor responsive to a change in electrical current tomaintain the electrical current below a threshold level.
 31. The systemof claim 30, wherein the first negative temperature coefficientthermistor and the first positive temperature coefficient thermistor areconnected in series between the power source and the sensor.
 32. Thesystem of claim 31, wherein the first negative temperature coefficientthermistor is electrically connected to a first node of the power sourceand wherein the first positive temperature coefficient thermistor iselectrically connected between the first negative temperaturecoefficient thermistor and the sensor.
 33. The system of claim 31,wherein the transient suppression and current control circuitry furtherincludes a second negative temperature coefficient thermistor and asecond positive temperature coefficient thermistor electricallyconnected in series between a second node of the power source and thesensor.
 34. The system of claim 30, wherein the one or more physicalcharacteristics include a change in a magnetic field detectable by thesensor.
 35. The system of claim 30, wherein the sensor and the transientsuppression and current control circuitry are incorporated into anintegral sensing device unit.